Airbag

ABSTRACT

An airbag including first and second sheets joined along outer peripheral parts. The second sheet includes a plurality of base cloths. The plurality of base cloths are arrayed around the circumferential direction, and include overlapping parts where adjacent ends are overlapping. At least one of the overlapping parts includes unjoined sections that are not joined together, and the gas inside the airbag can be ejected through the unjoined sections.

TECHNICAL FIELD

The present invention relates to an airbag adapted for deployment by gasgenerated by an inflator, and particularly relates to a vehicle airbag.

BACKGROUND ART

When collision energy acts on a vehicle, for example, a vehicle airbagdeploys in front of a vehicle occupant sitting in a driver seat or apassenger seat, thereby protecting the vehicle occupant.

Airbags of the type described have a vent hole. The vent hole is agas-releasing hole through which some of the gas is ejected to theexterior so as to restrict excessive increases in internal pressure whenthe airbag is deployed. The size of the vent hole is set in advance anddoes not change. Therefore, the ejection rate or quantity of gas ejectedto the exterior from the vent hole cannot be precisely controlled inaccordance with the state in which a vehicle occupant collides with thedeployed airbag.

From an initial stage in which the airbag begins to deploy in front ofthe vehicle occupant, the gas inside the airbag begins to be ejected tothe exterior through the vent hole. To increase the airbag's performanceof protecting the vehicle occupant, it is preferable that the internalpressure of the airbag be maintained over a long period of time.However, the ejection rate and quantity of the gas ejected to theexterior from the vent hole cannot be controlled.

Thus, an improvement can be made in regard to merely having a vent holein the airbag, in terms of precisely controlling the internal pressureof the airbag. In view whereof, techniques for controlling the internalpressure of an airbag have recently been developed (see Patent Document1, for example).

The airbag taught in Patent Document 1 has a vent hole cover for closingthe vent hole. This vent hole cover comprises a plurality of sewn partssewn into the airbag. The sewn parts sequentially rupture as theinternal pressure increases when the airbag is deployed, and therupturing concludes at the end of the airbag deployment. As a result,the vent hole cover is removed from the vent hole, and therefore thevent hole is opened. In other words, it is possible to control thetiming with which the gas inside the airbag is ejected to the exteriorfrom the vent hole.

However, in the airbag known in Patent Document 1, the size of the venthole is set in advance and does not change. Therefore, the ejectiontiming, ejection rate, and quantity of the gas ejected to the exteriorfrom the opened vent hole cannot be precisely controlled in accordancewith the state in which the vehicle occupant collides with the deployedairbag. Moreover, in the airbag known in Patent Document 1, since thevent hole cover for closing the vent hole is sewn, controlling theejection timing, ejection rate, and ejected quantity of the gas inaccordance with the state in which the vehicle occupant collides withthe deployed airbag inevitably makes the configuration complicated andcauses cost to increase.

PRIOR ART LITERATURE Patent Documents

-   [Patent Document 1] Japanese Patent Application Laid-Open    Publication No. 2007-302224

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a technique whereby theejection timing, ejection rate, and quantity of a gas ejected to theexterior from an airbag can be precisely controlled.

Solution to Problem

According to the invention, as defined in claim 1, there is provided anairbag comprising a first sheet near a protected object, and a secondsheet far from the protected object, wherein outer peripheral parts ofthe first sheet and the second sheet are joined, characterized in thatthe second sheet is formed by a plurality of divided base cloths, thebase cloths are arrayed along a circumferential direction and haveoverlapping parts where adjacent ends are overlapping, at least some ofthe overlapping parts have unjoined sections not joined together, andwhen the airbag deploys and the protected object collides therewith, agas can be ejected through the unjoined sections.

In the invention, as defined in claim 2, preferably, the second sheet iscircular in overall shape, each of the base cloths is formed into a fanshape with reference to a center of the circular second sheet, and theunjoined sections extend in a radial direction with reference to thecenter of the circular second sheet.

In the invention, as defined in claim 3, preferably, at least one valueamong the number of the unjoined sections, an overlap width of theoverlapping parts in the unjoined sections, and a length of the unjoinedsections is set such that the unjoined sections begin to open from astage in which the protected object collides with the deployed airbag.

In the invention, as defined in claim 4, preferably, the airbag of thesecond aspect is accommodated in a hub of a vehicle steering wheel, andthe unjoined sections are positioned such that at least some of theunjoined sections do not overlap a spoke of the vehicle steering wheelwhen the airbag deployed in a passenger compartment is viewed from afront side of the vehicle.

In the invention, as defined in claim 5, preferably, the unjoinedsections are plural in number, and the plural unjoined sections arepositioned evenly in the circumferential direction with reference to thecenter of the circular second sheet.

Advantageous Effects of Invention

In the invention, as defined in claim 1, the plurality of base cloths isarrayed along the circumferential direction and adjacent ends overlap,constituting the overlapping parts. At least some of the overlappingparts are configured as a plurality of unjoined sections which are notjoined together. These unjoined sections can be set so as to not open atthe internal pressure at the time the airbag has completely deployed.Therefore, the airbag can essentially preserve the deployed shape.

When the protected object (the vehicle occupant) collides with thedeployed airbag, the airbag deforms, whereby the unjoined sections openand excess gas inside the airbag can be ejected to the exterior.Therefore, the ejection timing, the ejection rate, and the quantity ofthe gas ejected to the exterior from the unjoined sections can beprecisely set (controlled) in accordance with the collision mode of theprotected object against the deployed airbag. Moreover, in order for theejection timing, the ejection rate, and the ejected quantity to be setaccording to the airbag, the configuration is simple, merely in which atleast some of the overlapping parts of the plurality of base cloths arenot joined. Examples of the collision mode include a first collisionmode in which the protected object collides with an outer peripheralpart of the deployed airbag, and a second collision mode in which theprotected object collides with a front surface of the deployed airbag.

In the invention, as defined in claim 2, the plurality of unjoinedsections extends in the radial direction with reference to the center ofthe circular second sheet. The shape of the airbag is changed by thecolliding protected object. As the shape changes, the plurality of basecloths is pulled in the circumferential direction about the center,along the surface of the second sheet. Since the unjoined sectionsextend in the radial direction with reference to the center, the pullingaction in the circumferential direction about the center can beeffectively utilized to begin to reliably open the unjoined sectionswith the proper timing.

In the invention, as defined in claim 3, due to at least one value amongthe number of the unjoined sections, the overlap width of theoverlapping parts in the unjoined sections, and the lengths of theunjoined sections being set in advance, the unjoined sections begin toopen from the stage in which the protected object collides with thedeployed airbag. Thus, the ejection timing, the ejection rate, and thequantity of the gas ejected to the exterior from the unjoined sectionscan be precisely set in accordance with the collision mode of theprotected object against the deployed airbag.

In the invention, as defined in claim 4, the unjoined sections arepositioned such that at least some of the unjoined sections do notoverlap the spoke of the steering wheel when the airbag deployed in thepassenger compartment is viewed from the front side of the vehicle.Therefore, when the gas inside the airbag is ejected to the exteriorfrom the unjoined sections, the ejected gas can flow into the passengercompartment without being blocked by the spoke. Consequently, excess gasinside the airbag can be quickly and reliably ejected to the exterior.

In the invention, as defined in claim 5, the unjoined sections areplurality in number. The plural unjoined sections are positioned evenlyin the circumferential direction about the center of the circular backsurface section. Therefore, the positional relationship of the pluralunjoined sections to the steering wheel does not change regardless ofthe steering state of the steering wheel, and the unjoined sections arealso positioned evenly in the circumferential direction relative to thesteering wheel. Consequently, no matter what area of the deployed airbagthe protected object collides with, the shape of the airbag locallycollapses (or deforms) readily. As a result, some of the unjoinedsections locally open readily, and ejection of the gas is begun readily.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing the interior of a vehicle equippedwith an airbag according to a first embodiment of the present invention;

FIG. 2 is a view of an enlarged configuration of the airbag shown inFIG. 1, as seen from the front side of the vehicle;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is an exploded view of the airbag shown in FIG. 3;

FIG. 5( a) is a view illustrating a configuration of a second unjoinedsection of FIG. 2;

FIG. 5( b) is a cross-sectional view taken along line b-b of FIG. 5( a);

FIG. 6 is a view showing the relationship between a steering wheel andthe airbag shown in FIG. 2;

FIGS. 7( a) through 7(i) are views illustrative of the operation of theairbag shown in FIG. 2; and

FIG. 8 is a view of an enlarged configuration of an airbag according toa second embodiment of the present invention as seen from the front sideof the vehicle.

DESCRIPTION OF EMBODIMENTS

Certain preferred embodiments of the present invention will be describedbelow with reference to the accompanying sheets of drawings.

First Embodiment

As shown in FIG. 1, a vehicle 10 is equipped with an airbag device 20.When collision energy acts on the vehicle 10, the airbag device 20causes an airbag 30 to be deployed into a passenger compartment 11 byhigh-pressure gas generated by an inflator 21 (see FIGS. 3 and 4). Theairbag 30 is deployed in front of a vehicle occupant Mn sitting in adriver seat 12, a passenger seat 13, or another seat such as rear seat(not shown), and the airbag 30 protects the vehicle occupant Mn byrestraining the vehicle occupant Mn. In the present embodiment, a devicefor protecting a vehicle occupant Mn (a driver Mn) sitting in the driverseat 12 is described as an example of the airbag device 20.

The airbag device 20 is described hereinbelow in detail. FIG. 2 showsthe airbag 30 as seen from the front side of the vehicle 10. The airbagdevice 20, as shown in FIGS. 3 and 4, is composed of the inflator 21, aretainer 22, a fixing ring 23, and the airbag 30, which are shown by theimaginary lines.

When the inflator 21 receives an ignite signal from a controller (notshown) due to collision energy acting on the vehicle 10, the inflator 21ignites a gas-forming agent, whereby high-pressure gas for deploying theairbag (hereinbelow referred to simply as “gas”) is generated andsupplied to the airbag 30. The inflator 21 has a mounting flange 21 a.The retainer 22 is a member for retaining the airbag 30 in a foldedstate and supporting the inflator 21, and is provided over a steeringwheel 14 (FIG. 1). The mounting flange 21 a is bolted to the retainer22, whereby the inflator 21 is fixed to a hub 14 a of the steering wheel14 shown in FIG. 1. As a result, the airbag 30 is accommodated in thehub 14 a of the steering wheel 14.

The airbag 30 is composed of a rear-side sheet (a first sheet) 31 and afront-side sheet (a second sheet or a back-surface section) 41. Both therear-side sheet 31 and the front-side sheet 41 are circular in overallshape. The circular airbag 30 is configured by the rear-side sheet 31and the front-side sheet 41 overlapping each other and outer peripheralparts 31 a, 41 a being joined together (sewn integrally at sutured parts42 in the outer periphery).

When the airbag 30 is deployed into the passenger compartment 11 asshown in FIG. 1, the rear-side sheet 31 is the section on the frontsurface (the bag rear half) that faces the vehicle occupant Mn beingprotected, and is configured from a single base cloth.

When the airbag 30 is deployed into the passenger compartment 11 asshown in FIG. 1, the front-side sheet 41 is the section on the backsurface (the bag front half) that does not come in contact with thevehicle occupant Mn, i.e., a section positioned so as to face thesteering wheel 14. Hereinbelow, the front-side sheet 41 is appropriatelyreferred to as the “back-surface section 41.”

Formed in the front-side sheet 41 are one inflator insertion hole 43 anda plurality of bolt holes 44. The inflator insertion hole 43 is disposedin the center CP of the front-side sheet 41 (the center CP of the airbag30, the center CP of the circle), and is a circular through-hole thatencircles the inserted inflator 21. The gas generated by the inflator 21is supplied into the airbag 30.

The plurality of bolt holes 44 is disposed in the periphery around ofthe inflator insertion hole 43. The front-side sheet 41 and the fixingring 23 are made to overlap the mounting flange 21 a of the inflator 21,and bolts 24 (see FIG. 4) inserted through the bolt holes 44 are screwedinto the mounting flange 21 a, whereby the airbag 30 is mounted to theretainer 22.

The front-side sheet 41 (the back-surface section 41) is a complexconfigured integrally from a plurality of divided base cloths 51 to 53.In the illustrated first embodiment, the front-side sheet 41 is formedby three base cloths 51 to 53. The plurality of base cloths 51 to 53 arearranged evenly along the sheet surface (the back surface) of thefront-side sheet 41, and only the ends (the borders) 51 a, 52 a, 53 a,which are adjacent in the circumferential direction, overlap each other.These overlapping sections 61 to 63 are hereinbelow referred to as“overlapping parts 61 to 63.” The respective overlapping parts 61 to 63are positioned evenly in the circumferential direction with reference tothe center CP of the circle.

When the deployed airbag 30 is viewed from the front side of the vehicle10 as shown in FIG. 2, with reference to the center CP of the circle,the point equivalent to 12:00 on a clock is designated as 0°, and theangle increases clockwise based on this point 0°. The plurality of basecloths 51 to 53 is appropriately referred to as the “first base cloth51,” the “second base cloth 52,” and the “third base cloth 53.” Thefirst base cloth 51 is positioned at the point 0°, and the second basecloth 52 and third base cloth 53 are positioned sequentially clockwise.

The first overlapping part 61 is a section where an end 51 a of thefirst base cloth 51 and an end 52 a of the second base cloth 52 overlapone another front-to-back. The second overlapping part 62 is a sectionwhere the end 52 a of the second base cloth 52 and an end 53 a of thethird base cloth 53 overlap one another front-to-back. The thirdoverlapping part 63 is a section where the end 53 a of the third basecloth 53 and the end 51 a of the first base cloth 51 overlap one anotherfront-to-back.

To be more specific, the plurality of base cloths 51 to 53 are formedinto a fan shape with reference to the center CP of the circle so thatthe front-side sheet 41 describes an overall circular shape. The centralangles θ1 of this fan are uniform or nearly uniform. The overlappingangles θ2 (overlap width) of the respective overlapping parts 61 to 63,where the plurality of base cloths 51 to 53 are adjacent to each other,are uniform or nearly uniform.

The overlapping angles θ2 are set to optimal values that take intoaccount the ejection starting pressure, the ejection rate, and thequantity of the gas ejected to the exterior from the airbag 30. Thefirst overlapping part 61 is positioned at the point 60°, the secondoverlapping part 62 is positioned at the point 180°, and the thirdoverlapping part 63 is positioned at the point 300°.

The overlap widths of the overlapping parts 61 to 63 may be uniform, forexample, rather than being set to the overlapping angles θ2.

The base cloths constituting the rear-side sheet 31 and the plurality ofbase cloths 51 to 53 are all composed of cloths, i.e., flexible panelsof the same material and the same thickness. These cloths have differentfriction characteristics (friction resistance) on the front and backsides. For example, the friction characteristics differ in the front andback sides due to a silicon coating being formed on one side of thecloth. The rear-side sheet 31 and the plurality of base cloths 51 to 53face each other with the sides that have low friction resistance.

The base cloths 51 to 53 will be described in greater detail. Each ofthe base cloths 51 to 53 is composed of a middle circular base part 54extending around the center CP, and a fan part 55 connected to an outerperiphery of the base part 54. The inflator insertion hole 43 and thebolt holes 44 are opened in the middles of the base parts 54. The baseparts 54 in the respective base cloths 51 to 53 are all made to overlapand are joined together (sewn integrally at a sutured part 45).Therefore, the strength of the inflator insertion hole 43 section in thefront-side sheet 41 increases.

The fan parts 55 each have an arcuate folding part 55 a and linearfolding parts 55 b, 55 b. The arcuate folding parts 55 a are arcuatefolding sections in which edges are formed by the arcuate edges of thefans being folded back toward the rear-side sheet 31. The arcuatefolding parts 55 a constitute the outer peripheral part 41 a of thefront-side sheet 41 shown in FIG. 3. The linear folding parts 55 b, 55 bare substantially linear folding sections in which edges are formed bythe edges at both circumferential ends of the fans (equivalent to theends 51 a, 52 a, 53 a in the circumferential direction of the pluralityof base cloths 51 to 53) being folded back toward the rear-side sheet31. The linear folding parts 55 b, 55 b are sutured so as to preservethe edged state.

FIG. 5( a) shows an enlarged view of a second unjoined section 62 ashown in FIG. 2. FIG. 5( b) is an enlarged cross-sectional view takenalong line b-b of FIG. 5( a).

At least some of the overlapping parts 61 to 63 are configured asso-called unjoined sections 61 a to 63 a, which are not joined together(not sewn integrally by a sutured part 65) as shown in FIGS. 2 and 5( a)and (b). These unjoined sections 61 a to 63 a are referred torespectively as a “first unjoined section 61 a,” the “second unjoinedsection 62 a,” and a “third unjoined section 63 a.”

These unjoined sections 61 a to 63 a are used in place of theconventionally known vent hole. The unjoined sections 61 a to 63 a areclosed during the normal state in which the internal pressure of theairbag 30 is nil or low, and are opened according to the increase ininternal pressure to be capable of ejecting gas when the internalpressure of the airbag 30 has reached a predetermined value. Theunjoined sections 61 a to 63 a have lengths Ln, the maximum valuesthereof being the entire length Ls of the ends 51 a, 52 a, 53 a in thecircumferential direction of the fan parts 55, and the lengths Ln areset to optimal values that take into account the ejection startingpressure, the ejection rate, and the quantity of the gas ejected to theexterior from the airbag 30.

The plurality of unjoined sections 61 a to 63 a shown in FIG. 2 arepositioned evenly in the circumferential direction about the center CPof the circle, and these sections extend in a radial formation withrespect to the center CP.

It is known that spokes 14 b of the steering wheel 14 are commonlypositioned mostly in the bottom half of the steering wheel 14 in asteering neutral state, as shown in FIGS. 1 and 6. In other words, thespokes 14 b are mostly positioned in the range of the points 90° to270°. Accordingly, the first overlapping part 61 and the first unjoinedsection 61 a are positioned at the point 60°, and the third overlappingpart 63 and the third unjoined section 63 a are positioned at the point300°, as described above. Therefore, when the airbag 30 deployed in thepassenger compartment 11 is viewed from the back surface, the pluralityof unjoined sections 61 a to 63 a are positioned such that at least someof the unjoined sections 61 a to 63 a do not overlap the spokes 14 b ofthe steering wheel 14.

Therefore, when the gas Ga inside the airbag 30 is ejected to theexterior from the first and third unjoined sections 61 a, 63 a, theejected gas Ga can flow into the passenger compartment 11 (see FIG. 1)without being blocked by the spokes 14 b. Consequently, excess gas Gainside the airbag 30 can be ejected to the exterior quickly andreliably.

Next, the operation of the airbag device 20 according to the firstembodiment will be described.

When at least a predetermined amount of collision energy acts on thevehicle 10 (see FIG. 1), the inflator 21 shown in FIG. 3 receives anignition signal and ignites the gas-forming agent, thereby generatinggas and supplying the gas to the airbag 30. The airbag 30 accommodatedin a folded up state on the steering wheel 14 (see FIG. 1) begins to bedeployed by the supplied gas. During the process of the airbag 30deploying, a cover (not shown) mounted on the steering wheel 14 rupturesfrom a tear line and forms an opening for the airbag 30 to projectthrough. As a result, the airbag 30 begins to deploy into the passengercompartment 11.

FIG. 7( a) schematically depicts the airbag 30 seen from the front sideof the vehicle 10, and corresponds to FIG. 2.

FIG. 7( b) shows a cross section taken along line b-b of FIG. 7( a).

FIG. 7( c) schematically depicts the airbag 30 when it has fullydeployed, and corresponds to FIG. 7( b).

FIG. 7( d) shows on enlarged scape the second unjoined section 62 ashown in FIG. 7( c).

FIGS. 7( e) through 7(g) illustrate a manner which the second unjoinedsection 62 a shown in FIG. 7( d) changes according to the increase ininternal pressure pb.

FIG. 7( h) schematically depicts the airbag 30 in the state of FIG. 7(g).

FIG. 7( i) shows on enlarged scape the second unjoined section 62 awhile opening in the state of FIG. 7( h).

During the initial state shown in FIGS. 7( a) and (b), when gas beginsto be supplied from the inflator 21 (FIG. 3) to the airbag 30, theairbag 30 deploys as the supplied gas quantity increases, and as aresult, deployment into the passenger compartment 11 (FIG. 1) completesas shown in FIG. 7( c).

As the internal pressure pb increases, the plurality of base cloths 51to 53 are pulled in the circumferential direction (in the direction ofthe arrows Te, Te) about the center CP of the circle, along the surfaceof the front-side sheet 41. However, the internal pressure pb of theairbag 30 at this state of deployment completion is comparatively low.Since the pressure difference between the inside and outside of theairbag 30 is small, the unjoined sections 61 a to 63 a are closed asshown in FIGS. 7( c) and (d). Therefore, there is a small leakagequantity of gas Ga inside the airbag 30 leaking out to the exterior fromthe unjoined sections 61 a to 63 a. In other words, merely with theairbag deployed, the internal pressure pb does not reach a certainreference pressure set in advance. Therefore, the airbag 30 essentiallypreserves its deployed shape.

The vehicle occupant Mn shown in FIG. 1 then collides with the airbag 30(a secondary collision). The airbag 30 changes shape due to the vehicleoccupant Mn colliding. As a result, the internal pressure pb of theairbag 30 further increases. Due to the internal pressure pb increasingto a reference pressure, the plurality of base cloths 51 to 53 arefurther pulled in the circumferential direction about the center CP ofthe circle, along the surface of the front-side sheet 41. Moreover,along with the shape change in the airbag 30, the plurality of basecloths 51 to 53 is further pulled in the circumferential direction aboutthe center CP of the circle, along the surface of the front-side sheet41.

Since the plurality of unjoined sections 61 a to 63 a extends in aradial formation with respect to the center CP of the circle, theoverlap widths θ2 of the overlapping parts 61 to 63 in the unjoinedsections 61 a to 63 a are reduced by the pulling action in thecircumferential direction about the center CP of the circle. In otherwords, the overlap widths θ2 shift so as to decrease in the sequenceshown in FIGS. 7( e) and (f). The unjoined sections 61 a to 63 a arethen completely opened as shown in FIGS. 7( g) and (h).

Thus, the unjoined sections 61 a to 63 a essentially begin to open fromthe stage in which the vehicle occupant Mn (the protected object Mn)collides with the deployed airbag 30. In other words, the unjoinedsections 61 a to 63 a open in the sequence of FIG. 7( f) and FIG. 7( g),and the excess gas Ga inside the airbag 30 is ejected to the exterior.FIG. 7( h) and FIG. 7( i) represent a state in which a large quantity ofexcess gas Ga inside the airbag 30 is ejected by the unjoined sections61 a to 63 a opening by a large amount. Due to the excess gas Ga beingejected to the exterior from the unjoined sections 61 a to 63 a,excessive increases in the internal pressure pb of the airbag 30 areprevented. As a result, the collision energy when the vehicle occupantMn collides with the airbag 30 can be efficiently alleviated.

Moreover, since the plurality of unjoined sections 61 a to 63 a extendin a radial formation with respect to the center CP of the circle, thepulling action in the circumferential direction about the center CP ofthe circle can be effectively utilized to begin to reliably open theunjoined sections 61 a to 63 a with the proper timing.

Furthermore, according to the first embodiment, the ejection timing, theejection rate, and the ejected quantity of the gas Ga ejected to theexterior from the unjoined sections 61 a to 63 a can be precisely setaccording to the collision mode of the vehicle occupant Mn (theprotected object Mn) colliding with the deployed airbag 30. There can beconsidered, for example, a first collision mode and a second collisionmode.

The first collision mode is a mode in which the head Hd of the vehicleoccupant Mn collides with the top end part (the outer peripheralsection) of the airbag 30 deployed as shown in FIG. 1. In this mode, thehead Hd collides with the outer peripheral section of the airbag 30 in aso-called radial direction from radially outward toward the center (inthe direction of arrow Fs), when the airbag 30 having been deployed intothe passenger compartment 11 is viewed from the vehicle occupant Mnside, as shown in FIG. 1, for example.

In the case of the first collision mode, the shape of the airbag 30readily collapses (or deforms) locally due to the collision energy (thesecondary collision energy) when the head Hd collides with the airbag30. As a result, the force whereby the base cloths 51 to 53 are pulledin the direction of the arrows Te, Te increases, as shown in FIG. 7.Therefore, some of the unjoined sections 61 a to 63 a locally openreadily, and the ejected quantity of the gas Ga ejected to the exteriorfrom the unjoined sections 61 a to 63 a therefore increases. A largequantity of the gas Ga is quickly ejected and the secondary collisionenergy is sufficiently absorbed, whereby a large amount of secondarycollision energy inflicted on the vehicle occupant Mn can besufficiently alleviated.

In the second collision mode, the chest Ch of the vehicle occupant Mncollides with the front surface of the airbag 30 deployed as shown inFIG. 1. In the case of the second collision mode, the shape of theairbag 30 is preserved comparatively readily despite the secondarycollision energy. Since the unjoined sections 61 a to 63 a open lessreadily than in the case of the first collision mode, the ejectedquantity of the gas Ga ejected to the exterior from the unjoinedsections 61 a to 63 a is smaller. Due to the smaller ejected quantity, alarge amount of secondary collision energy can be sufficiently absorbedby the entire airbag 30.

Thus, at least one value among the number of unjoined sections 61 a to63 a, the overlap widths θ2 of the overlapping parts 61 to 63 in theunjoined sections 61 a to 63 a, and the lengths Ln of the unjoinedsections 61 a to 63 a is set such that from the stage in which theairbag 30 expands and begins to contact the vehicle occupant Mn (theprotected object Mn), the unjoined sections 61 a to 63 a begin to openaccording to the increase in the internal pressure pb of the airbag 30.

As is clear from the above description, in the first embodiment, theplurality of base cloths 51 to 53 constituting the back surface of theairbag 30 is arranged along the back surface and only the adjacent ends51 a, 52 a, 53 a overlap each other, constituting the overlapping parts61 to 63. At least some of the overlapping parts 61 to 63 are configuredas unjoined sections 61 a to 63 a which are not joined together.

The ejection timing, the ejection rate, and the ejected quantity of thegas Ga ejected to the exterior from the unjoined sections 61 a to 63 acan be precisely controlled in accordance with the collision mode of thevehicle occupant Mn against the deployed airbag 30.

The overlap widths θ2 and the lengths Ln of the unjoined sections 61 ato 63 a may be set to separate values with each of the respectiveunjoined sections 61 a, 62 a, and 63 a.

Second Embodiment

An airbag according to a second embodiment of the present invention willnext be described. FIG. 8 shows the configuration of an airbag 30A ofthe second embodiment, seen from the front side of the vehicle 10 (FIG.1).

In the airbag 30A according to the second embodiment, a front-side sheet41A is formed by two base cloths 51A, 52A. The first base cloth 51A andthe second base cloth 52A are set in essentially the same size. The basecloths 51A, 52A have essentially the same configuration as the basecloths 51, 52 of the first embodiment.

First and second overlapping parts 61A, 62A have the same configurationas the first and second overlapping parts 61, 62 of the firstembodiment. The overlap widths Wr of the overlapping parts 61A, 62A havea certain width. First and second unjoined sections 61 aA, 62 aA havethe same configuration as the first and second unjoined sections 61 a,62 a of the first embodiment.

The first overlapping part 61A and the second overlapping part 62A arepositioned in point symmetry with each other with respect to the centerCP. For example, the first overlapping part 61A and the first unjoinedsection 61 aA are positioned at the point 165°, and the secondoverlapping part 62A and the second unjoined section 62 aA arepositioned at the point 345°.

The airbag 30A of the second embodiment having this configurationexhibits the same operation and effects as the airbag 30 of the firstembodiment. Furthermore, when the gas Ga inside the airbag 30A isejected to the exterior from the first and second unjoined sections 61aA, 62 aA, the ejected gas Ga can flow into the passenger compartment 11(FIG. 1) while being mostly unblocked by the spokes 14 b. Consequently,the excess gas Ga inside the airbag 30A can be quickly and reliablyejected to the exterior.

In first embodiment, the unjoined sections 61 a to 63 a are preferablyconfigured on at least some of the plurality of overlapping parts 61 to63. For example, the configuration may be one in which the firstunjoined section 61 a is provided in the first overlapping part 61 andthe third unjoined section 63 a is provided in the third overlappingpart 63, but an unjoined section is not provided in the secondoverlapping part 62. Similarly, in the second embodiment, unjoinedsections 61 aA to 63 aA are preferably configured on at least some ofthe plurality of overlapping parts 61A, 62A.

INDUSTRIAL APPLICABILITY

The airbags 30, 30A of the present invention are suitable for use in thevehicle airbag device 20 for restraining and protecting a vehicleoccupant Mn sitting in the driver seat 12 or the passenger seat 13 ofthe vehicle 10 by deploying in front of the vehicle occupant Mn.Furthermore, the airbags 30, 30A of the present invention are suitablefor use as side airbags for restraining and protecting a vehicleoccupant Mn sitting in the passenger compartment 11 by deploying to theside of the vehicle occupant Mn. Furthermore, the airbags 30, 30A of thepresent invention are suitable for use as pedestrian-protecting airbagsfor protecting pedestrians by being provided to the hood of the vehicle10, for example, and deploying to the vehicle exterior.

REFERENCE SIGNS LIST

-   -   10 Vehicle    -   14 Steering wheel    -   14 a Hub    -   14 b Spoke    -   30, 30A Airbags    -   31 Rear-side sheet (first sheet)    -   41 Front-side sheet (second sheet)    -   51-53, 51A, 52A Plurality of base cloths    -   61-63, 61A, 62A Overlapping parts    -   61 a-63 a, 61 aA, 62 aA Unjoined sections    -   CP Center of circular back surface    -   Ln Length of unjoined section    -   Mn Protected object (vehicle occupant)    -   pb Internal pressure of airbag    -   Wr, θ2 Overlap width

The invention claimed is:
 1. An airbag comprising a first sheet near aprotected object, and a second sheet far from the protected object,wherein outer peripheral parts of the first sheet and the second sheetare joined, characterized in that: the second sheet is formed by aplurality of divided base cloths; the base cloths are arrayed along acircumferential direction and have overlapping parts where adjacent endsare overlapping; at least some of the overlapping parts have unjoinedsections not joined together; and when the airbag deploys and theprotected object collides therewith, a gas can be ejected through theunjoined sections.
 2. The airbag of claim 1, wherein the second sheet iscirvular in overall shape, each of the base cloths is formed into a fanshape with reference to a center of the circular second sheet, and theunjoined sections extend in a radial direction with reference to thecenter of the circular second sheet.
 3. The airbag of claim 1, whereinat least one value among the number of the unjoined sections, an overlapwidth of the overlapping parts in the unjoined sections, and a length ofthe unjoined sections is set such that the unjoined sections begin toopen from a stage in which the protected object collides with thedeployed airbag.
 4. The airbag of claim 2, wherein the airbag isaccommodated in a hub (14 a) of a vehicle steering wheel, and theunjoined sections are positioned such that at least some of the unjoinedsections do not overlap a spoke of the vehicle steering wheel when theairbag deployed in a passenger compartment is viewed from a front sideof the vehicle.
 5. The airbag of claim 4, wherein the unjoined sectionsare plural in number and the plural unjoined sections are positionedevenly in the circumferential direction with reference to the center ofthe circular second sheet.